1. Field of the Invention
This invention relates generally to a method and system for evaluating a patient for shock, and specifically concerns a method and system for automatically determining probabilities of one or more shock types based on patient clinical and hemodynamic data.
2. Related Art
Shock is a life threatening situation which requires immediate attention and care. A wide range of illnesses can lead to shock. Shock can cause multiple organ failure. It can lead to life-threatening complications, such as heart failure. Therefore it is critical that the underlying illness, defining the type of shock, is determined and treated as quickly as possible.
Hemodynamically, all shock types are characterized by very low blood pressure and rapid heart rate. Other symptoms are, but not limited to, mental confusion, cool skin and rapid shallow breathing. Most shock cases can be classified into four major types: cardiogenic shock, hypovolemic shock, septic shock, and anaphylactic shock.
Cardiogenic shock is caused by heart malfunction or problem, which leads to inability to eject enough blood for the body needs. Cardiogenic shock is sometimes referred to as obstructive shock.
Hypovolemic shock is mainly due to massive blood loss or loss of body fluids, which, for instance, is caused by injury and subsequent bleeding, or sun stroke especially in elderly people.
Septic shock is the most critical type of shock. Bacteria are entering the blood stream, which leads to sepsis. Septic shock occurs when bacteria and their toxins damage tissues or organs in the body. Septic shock is equivalent to systemic inflammatory response syndrome (SIRS) secondary to a documented infection and describes a wide spectrum ranging from sepsis to severe sepsis to septic shock and multiple organ dysfunction syndrome (MODS).
Anaphylactic shock is caused by an allergic reaction of the body.
Each shock type requires a particular treatment. Mixed hemodynamic patterns of shock patients make classification of their shock type difficult, even more when considering a patient's life-threating condition and the limited time left to apply the right therapy. Traditionally, the differentiation of shock is performed by clinical assessments and investigations which are time consuming.
Rady [Mohamed Y. Rady: Bench-to-bedside review: Resuscitation in the emergency department”. Critical Care April 2005, 9, 2, 170-176] describes the challenge of assigning a patient in shock based on the plurality of hemodynamic parameters preload, filling pressures, end-diastolic volumes, cardiac output, afterload, systemic vascular resistance, systemic oxygen delivery, systemic oxygen consumption, systemic oxygen extraction ratio and global oxygen balance SVO2 or SCVO2.
Some of the shock types do not require comprehensive measurement of hemodynamic parameters because the reason for the shock is obvious. For instance, an injured patient exhibiting serious bleeding due to an accident is likely to develop a hypovolemic shock if not treated properly. For many acute illnesses, however, shock differentiation is more difficult. Clinical circumstances, such as lack of time or manpower, time consuming investigations or limited medical expertise can cause a delay or incorrect diagnosis and treatment which ultimately results in death.
The ratio of heart rate to systolic blood pressure has been described as the shock index, with a normal range of 0.5 to 0.7 in normal adults. It is used mostly to confine hypovolemic shock and it is not applicable in septic and cardiogenic shock, when heart rate is always increased in response to other factors.
The University of Pennsylvania, School of Veterinary Medicine has established a website on the Internet disclosing a technique for differentiating hypovolemic shock from the other types of shock. The suggested evaluation refers to review of the history, undertaking a complete physical exam, determination of external fluid loss (for instance, vomiting or blood loss) or internal fluid loss (for instance, fluid accumulation, internal bleeding), auscultation of the heart, evaluation of pulse quality and rhythm, ECG, chest X-Rays and evaluation for any evidence of infection, history of trauma, hypoxia, pancreatitis, burns or immunosuppression. These examinations and evaluations require time which is always a critical factor for shock patient, in particular in an emergency department which may be the first in line dealing with a shock patient.
U.S. Pat. No. 5,551,435 to Sramek discloses a method and system for therapeutic management relying on the patient's mean arterial blood pressure and stroke volume index but does not differentiate in any way between different shock conditions.
U.S. Pat. No. 6,776,764 to Pinsky discloses a method and apparatus for optimizing treatment of hemodynamically unstable patients based on measurements of arterial pressure and stroke volume of the patient and subsequent calculation of stroke volume variation, pulse pressure variation, mean arterial pressure, elastance and cardiac power. The method comprises treatment of the patient, including the administration of fluid infusions, vasoactive drugs or inotropic drugs. U.S. Pat. No. 6,776,764 references other patents related to this art which are incorporated by reference (U.S. Pat. Nos. 5,551,435; 5,584,298; 5,865,758; 6,280,390).
Assessment and differentiation of shock is a complex undertaking which usually requires rapid treatment. All aforementioned methods and apparatuses take a step-by-step approach to determine the type of shock.